Trying to remote wipe my old passcode locked 5s and can't get it online

so, I can't remember the passcode to my old phone I want to unlock. I don't have any computer and never synced it with iTunes. I think if I could use find my iPhone to erase it then I could restore it, but its not connected to my wifi and has no SIM card. I tried taking my straight talk SIM card out of my se, then was thinking I could use the iPad to erase it from find my iPhone. It shows that it has signal but says requires activation. sense it has signal I was thinking it was going to work but so far still says offline. I could try activating it, the number on the back of the phone may be all I need not sure, not sure if it's worth it. Any advise, any way it would connect to wifi without opening it?